The invention relates to a chain hoist for lifting, lowering and pulling loads, comprising:
a housing, in which a chain wheel, around which a load chain, provided at its end with a draw hook, is looped with form fit, and a shaft, which drives the chain wheel, preferably via a gear unit, are rotatably mounted;
a threaded disc, which, with its internal thread, is in screw connection with an external thread of the shaft, and is provided with a drive gear tooth system for engagement by a force element moved by manual or motorized means;
a brake disc, which is rotatable with respect to the shaft and the threaded disc, having a first braking surface, which is facing a drive surface rotationally fixed to the shaft, and a second braking surface, which is facing the threaded disk, and having locking teeth, arranged on the brake disc, for the unilaterally blocking engagement of a safety catch mounted at n the housing;
a freewheel device, which is configured to increase the axial distance between threaded disc and drive surface.
Components of such a chain hoist, as disclosed in a typical design in U.S. Pat. No. 4,512,555, are a housing provided with a hook as the abutment element, a drive shaft rotatably mounted in the housing, an actuating lever that can be coupled to the drive shaft, and a chain wheel, which can be set in rotation by the drive shaft and over which the load chain of the chain hoist, which load chain is provided with a hook, is guided. The actuating lever can be coupled to the drive shaft via a detent mechanism. In addition, chain hoists of this type usually have a freewheel device that, when switched on, decouples the drive shaft from the actuating lever or the detent mechanism.
Primarily, these chain hoists are used to lift or lower loads. For this purpose, in the case of a manually operated chain hoist, the actuating lever thereof is pivoted back and forth, wherein the chain wheel, just with the one movement, is successively further rotated by the integrated detent mechanism and in this way raises or lowers the load chain with the weight load hanging therefrom. Chain hoists of the generic type further possess a freewheel device which can be manually switched on. In the freewheel setting, the chain can be freely pulled through in one or the other direction. In addition, chain hoists of this type possess a self-acting load pressure brake. This is a mechanism which prevents the freewheel device from being switched on when a load is still hanging from the chain wheel and therefore a minimum torque is present at the drive shaft. The load pressure brake prevents the drive shaft, and hence the weight load, from being released by accidentally switching on the freewheel action.
The same chain hoists are frequently also used for other load tasks. One example is installation work on overhead power lines. When installing the power lines, they have to be tensioned first and then suspended from current insulators. Because of the particular localities, such work can only be performed by specialist technicians. In this context, there have been extreme situations, above all upon the occurrence of strong gusts of wind, in which, after the freewheel action had been switched on since no load was any longer present, tensile forces nevertheless arose in the load chain, possibly due to swaying of the chain hoist, associated with a pay-out of the chain. When this pay-out occurred with increasing speed, a violent flapping of the free chain ends (whip effect) occurred additionally, associated with a considerable risk of injury for the technician.
The object of the invention is to make a contribution to defusing dangerous, albeit only rarely occurring, extreme situations, as they arise primarily when the freewheel action is switched on, by means of technical measures on the chain hoist.